He was already "majoring in minors" in 1990. AO 1990 was the only tier 1 final he reached. Edberg/Becker/Agassi were the rulers of the game (no Courier yet + of course Sampras "out of the blue" breakthrough at USO)
Ah. I don't read the "tier 1" as meaning very much back then (although it was the first year of the new designation on the ATP Tour). Lendl didn't even play any of Monte Carlo, Hamburg, Rome, Canada, Cincinnati, and Stockholm.
Becker had a pretty mediocre year in 1990 in a lot of ways. Had Edberg had a decent run at the US Open rather than losing in round 1 (his loss in round 1 of Roland Garros was forgivable, especially as he played future two-time winner Bruguera) and had Agassi won at least one of the Roland Garros and US Open finals, then I think we'd have had to say that Edberg and Agassi were the two dominant players of the year. Edberg and Agassi played each other in the finals of Indian Wells, Miami, and the World Championships, while Edberg was in the final of the Australian Open and Wimbledon and Agassi in the final of Roland Garros and the US Open. Times were different then and players were more even. But Edberg and Agassi were the players who put in the largest number of consistent results in 1990. Their position as the top two players was partially obscured by:
1) Edberg being injured in the final of the Australian Open and so not winning a match he'd almost certainly have won were he fit.
2) Agassi blowing two major finals that he went into as firm favorite.
3) Edberg losing in round 1 of two majors, one of which he went into on a 21-match unbeaten run and in which he really should have at least made the semis, probably the final, and possibly won.
4) Agassi skipping two majors.
Here's what they did do:
1) Edberg won seven titles (Indian Wells, Tokyo Outdoor, Wimbledon, Los Angeles, Cincinnati, Long Island, Paris Bercy) from 12 finals (also Australian Open, Miami, Sydney Indoor, Stockholm, and the World Championships. That gives Edberg two more titles than anyone else and several more finals.
2) Agassi won four titles (San Francisco, Miami, Washington, and the World Championships) from seven finals (also Indian Wells, Roland Garros, and the US Open).
I don't think Edberg and Agassi quite were the two dominant players, but, as I said, had Agassi won Roland Garros or the US Open and Edberg made a deep run at the US Open, then I think there'd be a case for saying that they were.